Ladder and method of manufacture thereof



July 8, 1969 P. J. PELLANDINE 3,454,130

7 LADDER AND METHOD OF MANUFACTURE THEREOF Filed Nov. 8, 1967 UnitedStates Patent US. Cl. 18246 Claims ABSTRACT OF THE DISCLOSURE A ladderconsisting of side rails each constructed from a pair of plastic rodsjoined in parallel relationship to each other by metal plates engagingthe rods and the metal plates of one side rail joined by rungs to themetal plates of the other side rail.

This invention relates to an improved ladder and the method of itsmanufacture.

Ladders of various kinds are known and ladders of fixed length or of theextension type have been made from timber or metal.

When ladders are required to be movable for use at various places, it isessential that these ladders be as light as possible. In some cases,such as for use by electric supply authorities, it is also essentialthat the ladders be non-electrical conductors. Wooden ladders are morefavoured by electric supply authorities than are metal ladders.

Many attempts have been made to make a ladder from plastic but the costof such ladders have been prohibitive. Ladders have been made by usingchannel shape fibre glass side rails to reduce the quantity of plasticbut these have also been found to be too costly. Many problems have beenmet in trying to utilise a combination of metal and plastic in laddermanufacture. The main problem has been to find suitable means ofinterlocking the metal and the plastic in a ladder construction.

The objects of this invention are to provide a ladder made from partmetal and part plastic.

According to this invention an improved ladder may be said to compriseplastic side rail members connected by metal plates to rungs.

It is preferred that each plastic side rail member be composed of twofibre glass plastic rods of circular cross section. It is not essentialthat rods be used because tubular sections could also be used.

For the invention to be more clearly understood, an embodiment of theinvention is described hereafter in some detail with reference to, andas illustrated in the accompanying drawings, in which:

FIG. 1 shows perspective view of a section of the ladder and,

FIG. 2 is a cross-sectional view showing a metal plate on each end of arung engaged in the slots of the side rail rods.

In this embodiment each side rail of the ladder 12 consists of two threequarter inch diameter fibre glass rods 13 slotted at spaced intervalsalong their length. The distance between the centre line of one slot tothe centre line of an adjacent slot in each rod 13 is equal to thecentre line distance between the rungs of the ladder. In this particularembodiment the length of the slots is five and a half inches. The widthof the slots are of size to accommodate the thickness of metal plates 14(which in this embodiment is 12 B.S.G. commercial aluminium plate) andthese plates 14 are secured by welding or the like to tubular rungs 15.Each metal plate 14 at one end of the rung 15 is secured by an epoxyresin to a slot 16 of each of two of the fibre glass rods 13 so that thetwo fibre glass rods are held in parallel spaced relationship to eachother and thereby form one side rail 10 of the ladder 12. Similarly themetal plates 14 at the other end of the rungs are secured to the slotsof the other two fibre glass rods 13.

To improve the bond between the metal plates 14 and the fibre glassplastic rods 13 the portion of the metal plates, which is enclosedwithin the slot 16 of the plastic rod, is treated by solvent cleaning,sand blasting or chemi cal pickling. The portion of the metal platewhich is to be closed may be apertured at one or more places to therebyallow a slug of epoxy resin to extend through the aperture from thewalls of the slot.

The slots may be readily formed by a milling and/or slotting machine.

A method of making a ladder according to the invention may be said tocomprise the steps of welding a metal plate one to each end of, andtransverse to the longitudinal axis of a metal rung, forming slots infour plastic rods at spaced intervals along their length, the width ofsaid slots being substantially equal to the thickness of said metalplates, positioning the plastic rods such that the slots in said rodsare engagedby the metal plates to thereby form two side rails of theladder and said metal plates secured to said side rails by an epoxyresin previously applied to said slots.

When the metal plates 14 and rungs 15 are Duralumin or the like it hasbeen found that the ladder so formed has a weight approximately twothirds that of a wooden ladder of equivalent size. As the metal parts ofthe ladder do not form a continuous path throughout the length of theladder, the ladder has the required non-electrical conductivitycharacteristics.

Of course, it will be realised that two separate ladders of thisinvention may be arranged together in the well known extension laddercombination.

Thus it will be seen that the invention has provided a lightweightladder of considerable merit.

What I claim is:

1. A ladder comprising electrically non-conductive plastic side rails,each side rail consisting essentially of a pair of fibre glass rods heldin spaced relationship to each other by metal plates having oppositelydisposed edge portions fixedly engaging matching longitudinal slots insaid fibre glass rods at spaced intervals along the length of each fibreglass rod, said edge portions being bonded to the interior surface ofsaid longitudinal slots by an epoxy resin; and metal rungs connectingthe metal plates of one side rail to the corresponding metal plates ofthe other side rail.

2. A ladder according to claim 1 in which the fibre glass rods are ofcircular cross-section.

3. A ladder according to claim 1 in which the metal plates arecommercial aluminium plate and the rungs are tubular aluminium and arewelded to the plates.

4. A ladder according to claim 1 in which the edge portion of the metalplates engaging the slots in the fibre glass rods has been speciallyprepared to provide an improved bond with epoxy resin by a process ofeither solvent cleaning, sand blasting, chemical pickling, beingapertured in at least one place, being indented in at least one place,or a combination thereof, before being bonded by said epoxy resin to theinterior surface of said longitudinal slot to eifect a stronger fixedengagement therewith.

5. A method of making a ladder comprising the steps of:

(a) welding metal plates one to each end of, and

transverse to, the longitudinal axis of at least one metal rung;

(b) forming slots in four plastic rods at spaced intervals along theirlength, the slots being on the same side of said plastic rods, the widthof said slots being substantially equal to the thickness of said metalplates;

(c) applying epoxy resin to the internal surfaces of said slots;

(d) positioning the plastic rods such that the slots containing saidepoxy resin in respective pairs of said rods are engaged by therespective metal plates to thereby form two side rails of the ladder,said side rails being secured together by said at least one metal rung;and

(e) allowing said epoxy resin to cure whereby said ladder becomes aunitary, electrically non-conducting ladder.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 3/1949 GreatBritain. 5/1908 Austria.

REINALDO P. MACHADO, Primary Examiner.

US. Cl. X.R.

